It is especially common with paper bag manufacturing to pre-groove the fold lines in order to obtain clean folds. The grooving device described in FIG. 4 of French PS 13 64 183 for forming the fold lines which divide off the inward-folding side panels of raised crossed-bottoms of crossed-bottom sacks provides an example of how the fold lines formed through grooving slant towards the outside, because the sack material is pulled into the groove by the grooving disc.
The phenomenon of the sack material being pulled into the center of the sack during the formation of the fold lines which divide off the side flaps of raised cross-bottoms is described in German PS 12 99 514. It was suggested in this publication to set up a powered press-roller on the free running sides of the workpiece next to the grooving disc, which would run off of cylindrical sections of discs equipped with grooving slots and would exert outwardly-directed tension on the material ends. However, the device described in German PS 12 99 514 requires increased structural expenditure, in that the press-roller running off of a cylindrical section of the grooving disc is mounted on an angled lever which swivels in the machine housing and is supplementally equipped with its own drive.